"Women have caught up with men in the amount of alcohol they drink," The Guardian reports. A survey of data from around the world suggests the gap between men and women is closing rapidly when it comes…

"Women have caught up with men in the amount of alcohol they drink," The Guardian reports.

A survey of data from around the world suggests the gap between men and women is closing rapidly when it comes to alcohol use and subsequent alcohol-related harms.

Researchers looked at 68 studies from across the world studying people born from 1891 to 2000 to examine changing trends in alcohol use in men and women.

In the early 1900s, men were twice as likely as women to drink alcohol and three times more likely to experience alcohol-related problems. Now, there is far less of a difference, so the genders have very nearly equalised.

Despite the many suggestions mooted in the media – such as the influence of "90s ladette culture" – the study did not investigate the reasons behind the rise.

The authors suggest the findings indicate the need to particularly focus on young women to reduce the impact of alcohol use and related harms.

Women are more vulnerable to the harmful effects of alcohol because of a number of factors, such as the fact it takes longer for their bodies to break down alcohol.

To keep health risks to a low level, both men and women are advised to drink no more than 14 units a week.

Where did the story come from?

The study was carried out by researchers from the Australian NHMRC Centre of Research Excellence in Mental Health and Substance Use at the University of New South Wales, Australia, and Columbia University Mailman School of Public Health in the US.

It was funded by the Australian Government under the Substance Misuse Prevention and Service Improvements Grant Fund and a National Health and Medical Research Council Centre of Research Excellence Grant. The authors declare no competing interests.

The media generally reported the story accurately. However, despite many suggestions provided by the media and independent experts, the study did not investigate why these trends have changed.

One hypothesis put forward by the researchers is that more women are now working than 50 years ago, so they have an independent income. This may mean they are free to socialise as they wish without having to rely on their partner.

What kind of research was this?

This systematic review and meta-analysis aimed to summarise published literature on changes across time of male-to-female ratios in key indicators of alcohol use and related harm.

While meta-analyses are a useful way of pooling research in an area, they are only as good as the individual studies included.

In this case, 68 studies were included in total:

48 repeated cross-sectional studies

19 single cross-sectional studies

1 longitudinal study

These study designs can provide observational information from a single point in time or show how things have changed over time, but they can't provide answers to explain the trends.

There may also be some inaccuracies in terms of how representative the populations were or the information on frequencies of alcohol use.

What did the research involve?

The review used accepted quality standards for performing a systematic review. Studies including regional or nationally representative populations were identified.

Separate data for males and females was given on at least one of the following key indicators of alcohol use and harms:

lifetime or current alcohol use disorder – for example, dependence

alcohol-related problems – for example, drunkenness or other negative consequences

alcohol-related treatment

seeking stages in the alcohol use and related problems cycle – for example, onset of use or transition from use to disorder

heavy episodic or binge drinking

Researchers pooled the data from 68 relevant international studies published between 1980 and 2014, including a comparison of male and female drinking patterns.

The studies included collected data between 1948 and 2014, and included 4,426,673 people born as far back as 1891 and up to 2000. Of those, just over a third each were from North America and Europe.

The births were grouped into five-year cohorts from 1891 to 2000, except for the first (1891-1910) and last (1991-2000), generating 1,568 sex ratios. The study quality was assessed by two independent moderators.

The male-to-female ratios were calculated for three broad categories:

any alcohol use

problematic alcohol use

alcohol-related harms

The meta-analyses resulted in pooled sex ratios within these three categories for each birth cohort.

What were the basic results?

The pooled data showed that the gap between men and women consistently closed across all three categories of any alcohol use, problematic alcohol use and alcohol-related harms:

alcohol use – the sex ratio of men to women was 2.2 (95% confidence interval [CI] 1.9 to 2.5) in the 1891-1910 birth cohort, indicating men were two times more likely to report any alcohol use compared with their female counterparts; this decreased to a low of 1.1 (95% CI 1.1 to 1.2) for those born between 1991 and 2000

problematic alcohol use – the sex ratio decreased from 3.0 (95% CI 1.5 to 6.0) in the 1891-1910 cohort to 1.2 (95% CI 1.1 to 1.4) in those born between 1991 and 2000

alcohol-related harms – the sex ratio decreased from 3.6 (95% CI 0.4 to 30.4) in the 1911-15 birth cohort (no earlier data) to 1.3 (95% CI 1.2 to 1.3) in those born between 1991 and 2000

For all three broad categories, sex ratio declined by 3.2% every five years across birth cohorts after accounting for potential bias. However, it was steepest in cohorts born from 1966 onwards.

How did the researchers interpret the results?

The researchers concluded that, "Alcohol use and alcohol use disorders have historically been viewed as a male phenomenon.

"The present study calls this assumption into question, and suggests that young women in particular should be the target of concerted efforts to reduce the impact of substance use and related harms."

They also said: "That the birth cohort effect on sex ratios has become more pronounced in these recent birth cohorts points to the value of continuing to focus research on adolescent and young adult sex-specific trends in substance use.

"Given that this young age group are relatively early in their alcohol use careers, these findings highlight the importance of further tracking young male and female cohorts as they age into their 30s, 40s and beyond."

Conclusion

This review provides support that the male-female gap in indicators of alcohol use and related harms has been closing. This is more evident in young adults, and has changed quicker in more recent years.

While the study provides evidence of a continuing trend, there are some key limitations.

The review can provide observations of trends over time, but cannot tell us the reasons behind the closing of the alcohol use gap.

It did not examine, for example, whether the changes in sex ratios in alcohol use and alcohol-related harms are the result of a fall in prevalence among men or a rise in women.

The authors speculated about some of the reasons behind this narrowing sex difference.

They suggested it could be down to the female gender role changing over time – for example, the increasing participation of women in the labour force, better education, and increased age of first marriage.

They also suggested broader social, cultural and economic changes might be involved.

Another important limitation is that these estimates may be imperfect. The studies included were all assessed for quality, though are likely to have varied widely in their inclusions, methods and follow-up.

For example, the majority of studies were from the US and Europe, but we can't say they'd be applicable to all populations.

The questions used to assess alcohol use and problems are also likely to have varied widely across studies, and across the century that the study covered.

Participants may also not have been fully reliable in their responses – which again could have differed over the years.

For example, it's possible that women in the earlier part of the 1900s may have been less willing to report excess alcohol consumption because of social perception, even if they did drink higher quantities of alcohol.

Overall, this is a good data set and likely to be the best we can get on this question, but the data still really needs to be considered to be estimates and not definite figures.

To keep health risks from alcohol to a low level if you drink most weeks:

men and women are advised not to drink more than 14 units a week on a regular basis

spread your drinking over three or more days if you regularly drink as much as 14 units a week

if you want to cut down, try to have several drink-free days each week